1. Field of the Invention
This invention relates to an electronic control system for the internal combustion engine of a type, in which those values related with the atmospheric pressure such as the atmospheric pressure value, and so forth are found by computation of other control parameters of the internal combustion engine, and by use of these computed values as the auxiliary parameters for the control of the engine.
2. Discussion of Background
In the following, a conventional electronic control device for the internal combustion engine will be explained in reference to FIGS. 1 and 2 of the accompanying drawing which illustrate one preferred embodiment of the electronic control system according to the present invention.
In FIG. 1, a reference numeral 1 designates an internal combustion engine which is mounted on an automobile, for example, and in which only one cylinder is shown out of a plurality of cylinders; a numeral 2 refers to a cylinder of the internal combustion engine; a numeral 3 refers to an air inlet valve to be actuated by a cam (not shown in the drawing); a reference numeral 4 denotes an intake manifold of the internal combustion engine 1; a numeral 5 refers to an injector provided on each cylinder of the intake manifold 4; a reference numeral 6 represents a surge tank connected to the upstream side of the intake manifold 4; a numeral 7 refers to a throttle valve provided in the air inlet passage at the upstream of the surge tank 6 and for controlling the quantity of intake air into the internal combustion engine 1; a reference numeral 8 denotes a sensor connected to the throttle valve 7 and for detecting a degree of opening of the throttle value 7; a numeral 9 refers to a bypass which functions to detour both upstream and downstream of the throttle valve 7; a reference numeral 10 designates a bypass air quantity regulator provided in the bypass 9; a reference numeral 11 denotes a hot-wire type air-flow sensor (hereinafter abbreviated as "AFS") which is provided at a location further upstream of the throttle valve 7 and for detecting a flow rate of air to be taken into the internal combustion engine by means of, for example, a temperature-dependent-resistor; a reference numeral 12 indicates an air temperature sensor for detecting temperature of the inlet air before it passes through the AFS 11; a numeral 13 refers to an air cleaner provided at an inlet port situated at a position further upstream of the AFS 11 and the intake air temperature sensor 12; a numeral 14 refers to a water temperature sensor which is provided in the cooling water passage of the internal combustion engine 1 and for detecting temperature of the water; a reference numeral 15 denotes a crank angle sensor for detecting a predetermined crank angle of the internal combustion engine 1; a numeral 16 refers to a neutral detection switch for detecting that no load is imposed on the internal combustion engine 1; and a reference numeral 17 designates an electronic control unit (hereinafter abbreviated as "ECU") which determines a fuel injection quantity based on output signals mainly from the AFS 11, the water temperature sensor 14 and the crank angle sensor 15, and controls the injector 5 in synchronism with the output signal from the crank angle sensor 15 to thereby carry out the fuel injection, at which time each of the output signals from the throttle opening degree sensor 8, the air temperature sensor 12 and the neutral detection switch 16 is used in the ECU as the auxiliary parameter. The ECU 17 also controls the bypass air quantity regulator 10, although the details of its operation are omitted.
FIG. 3 is an enlarged schematic diagram of the air intake section shown in FIG. 1. In the drawing, Ta denotes an atmospheric temperature; Pa represents an atmospheric pressure; Qa designates an air flow rate to be measured by the AFS; .theta. denotes a degree of opening of the throttle valve 7; S(.theta.) indicates an area for the air passing through the throttle section when the degree of opening of the throttle valve is .theta.; and Ps denotes an internal pressure of the surge tank 6.
FIG. 8 is a block diagram showing the internal structure of the ECU in the conventional electronic control system, while FIG. 9 is a graphical representation with a pressure ratio Pa/Ps being taken on the abscissa and with a value "f" to be explained later being taken on the ordinate.
The conventional electronic control system of the above-described construction is disclosed in, for example, unexamined Japanese Patent Publication No. 162341/1984.
In the following, explanations will be given as to the operations of this conventional electronic control system. A function generator 17a, which has introduced therein an input signal .theta. of the throttle valve opening degree as detected by and outputted from the throttle valve opening degree sensor 8, produces, as an output therefrom, a signal of a ratio of an air flow rate value Q.sub.0 with respect to the atmospheric pressure value P.sub.0 under the reference atmospheric condition in correspondence to the input signal into the function generator. This signal is introduced as an input into a division circuit 17b together with an air flow rate signal Qa, and a value of Qa.div.(Q.sub.0 /P.sub.0). An output from this division circuit 17b corresponds to a value Pa.f. Here, the following equation will be established with K as a ratio of specific heat: ##EQU1## The value of Pa.f is introduced into the division circuit 17d together with the air inlet tube pressure signal Ps to be obtained from an input terminal 17c. A signal obtained from the division circuit 17d is introduced as an input into a subsequent comparison unit 17e where a pressure ratio of Ps/(Pa.f) and a fixed value "a" of, for example, 0.52828 are compared. As it will be seen from reference to FIG. 9, in a region of M (Mach number)=1 (which is below the fixed value "a" on the march of Ps/Pa=a), there takes place a sonic choke and the value "f" takes a constant value; on the other hand, in a region of M&lt;1 (which is above the value "a"), the value "f" varies. On account of this, a switch 17f is opened or closed in accordance with the result compared by the comparison unit 17e. If Ps/(Pa.f)&lt;a, there is established, from the graphical representation of FIG. 9, a hypothesis of f=1, for example, and the switch 17f is closed, whereby the atmospheric pressure value Pa is produced as an output from the division circuit 17b by way of the switch 17f. In the case of Ps/(Pa.f).gtoreq.a, the switch 17f is opened, because no hypothesis of, for example, f=1 is established.
The conventional electronic control system for the internal combustion engine is constructed as described in the preceding, wherein use is made of a phenomenon such that the value "f" becomes constant in the region of M=1 for the purpose of finding out the atmospheric pressure value, hence the value is limited to a region where a relationship of Ps/Pa&lt;0.52828 is established, i.e., the engine idling time. However, there was a point of problem such that, during the engine idling time, the engine operation was remarkably influenced by temperature, fluctuation in the degree of opening of the throttle valve, fluctuation in the air flow rate through the bypass at the time of total closure of the throttle valve, whereby precision in the atmospheric pressure value to be obtained was not satisfactory. For example, with the internal combustion engine having a displacement of 2 liters, the air flow rate during the engine idling is 3 g/sec., in contrast to which the leakage flow rate at the throttle section is up to about 0.5 g/sec. Moreover, a constant in a computation equation to find out the air flow rate from the degree of opening of the throttle valve and the internal pressure of the surge tank is a function of the air temperature which is substantially proportionate to a root value of an air temperature ratio. Furthermore, an error of the degree of opening of the throttle valve is also innegligible for the error, because of the air flow rate being small during the engine idling.